A deep seismic transect from Hovgård Ridge to northwestern Svalbard across the continental-ocean transition: A sheared margin study
A deep seismic transect from Hovgård Ridge to northwestern Svalbard across the continental-ocean transition: A sheared margin study
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从 Hovgård 海岭到斯瓦尔巴群岛西北部跨越大陆-海洋过渡区的深地震横断面：剪切边际研究
DOI：
10.1111/j.1365-246x.2004.02204.x
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发表时间：
2004
影响因子：
2.8
通讯作者：
Y. Nishimura
中科院分区：
文献类型：
--
作者：
O. Ritzmann;W. Jokat;W. Czuba;A. Guterch;R. Mjelde;Y. Nishimura
在 RV Polarstern 的 ARK15/2 巡航航段期间，在斯瓦尔巴群岛西部大陆边缘 Kongsfjorden（Ny ?lesund）收集了新的地震折射数据。利用陆上和海上地震接收器和密集的气枪射击模式，可以详细了解斯瓦尔巴群岛大陆内部、大陆-海洋过渡区以及与北部克尼波维奇海岭和莫洛伊海岭有关的洋壳的速度结构。斯瓦尔巴群岛的加里东中部和西部地体在地震速度结构的基础上无法区分。在 7 至 8 公里厚的古生代沉积盖层下方，结晶地壳揭示了地震速度在 6.1 至 6.9 公里/秒之间的三层结构。地体之间的地质缝合线是难以察觉的。第三纪 Forlandsundet 地堑下方的中、上地壳显示出惊人的低速度。这可能与斯瓦尔巴群岛和格陵兰岛北部之间的早古生代汇聚挤压运动有关，随后是伸展（松弛）阶段。我们认为，地堑下方存在脆性破裂岩层，该岩层还埋藏着沉积古生代核心。大陆-海洋过渡可以归类为在斯匹次卑尔根断裂带大陆部分形成的剪切边缘。仅在 Forlandsundet 地堑下方的低速区以西，地壳适度变薄。这导致了这样的假设：渐新世以来的张拉裂谷运动与斯瓦尔巴群岛的中央地体脱钩。莫霍面在大陆-海洋过渡带向东倾斜 45°，大陆一侧的地震速度较高，为 7.2 km/s。这些可以解释为轻微的地幔侵入，可能是由于冷大陆岩石圈和热海洋岩石圈并置而引起的对流引起的。与全球平均水平相比，克尼波维奇海脊和莫洛伊海脊生成的洋壳很薄（2至4公里），其特点是缺乏大洋第3层。这些观测结果可归因于上升地幔的传导冷却，这是由于极低的分歧率和邻近的冷大陆地壳。克尼波维奇海岭段下方的下伏地幔略有蛇纹石化，反映为约 7.7 公里/秒的低地震速度。在莫洛伊海岭洋段观察到更厚的同裂谷和裂谷后沉积物和沉积岩序列，这是由于相对于克尼波维奇海岭段更大的沉降造成的。
New seismic refraction data were collected across the western Svalbard continental marginoff Kongsfjorden (Ny ?lesund) during the cruise leg ARK15/2 of RV Polarstern. The use ofon- and offshore seismic receivers and a dense airgun shot pattern provide a detailed viewof the velocity structure of SvalbardOs continental interior, the continent-ocean transition,and oceanic crust related to the northern Knipovich Ridge and the Molloy Ridge.The Caledonian central and western terranes of Svalbard are not distinguishable on the basisof seismic velocity structure. Below a 7 to 8 km thick Paleozoic sedimentary cover the crystallinecrust reveals a three-layer structure with seismic velocities ranging between 6.1 and 6.9 km/s.The geological suture between the terranes is imperceptible. The middle and upper crust belowthe Tertiary Forlandsundet Graben shows striking low velocities. This can be related to theEarly Paleozoic convergent transpressive movements between Svalbard and northern Greenland,followed by an extensional (relaxing) phase. We argue that a brittle-fractured rock formation ispresent below the graben, which also buries a sedimentary Paleozoic core.The continent-ocean transition can be classified as a sheared margin formed at the continentalpart of the Spitsbergen Fracture Zone. Moderate crustal thinning is achieved only to the westof the low velocity zone below the Forlandsundet Graben. This leads to the assumption thattranstensional rift movements since Oligocene were decoupled from the central terraneof Svalbard. The Moho dips with an angle of 45° eastwards at the continent-ocean transitionthat exhibits higher seismic velocities of 7.2 km/s on the continental side. These can beinterpreted as minor mantle-derived intrusions, probably induced by convection due to thejuxtaposition of cool continental and hot oceanic lithosphere.The oceanic crust generated at the Knipovich Ridge and the Molloy Ridge is thin (2 to 4 km),compared to the global mean, and is characterised by the absence of oceanic layer 3. Theseobservations can be ascribed to conductive cooling of the ascending mantle due to theextremely low divergence rate and the neighbouring cool continental crust. The underlyingmantle is slightly serpentinized below the Knipovich Ridge segment, reflected by low seismicvelocities of ~7.7 km/s. A thicker sequence of syn- and post rift sediments and sedimentaryrocks are observed on the Molloy Ridge oceanic segment, which results from greater subsidencerelative to the Knipovich Ridge segment.